Process for refining lead



July 15, 1958 HOFFMANN 2,843,476

PROCESS FOR REFINING LEAD Filed April 25, 1953 Inventor Attorney United States Patent PRocEss son nEruNiNo LEAD Markus Hoifmann, Purley, England, assignor to H. J. Enthoven & Sons Limitcd,'London, England, a British company Application April 23, 1953, Serial No. 350,642

Claims priority, application Great Britain May 2, 1952 4 Claims. (Cl. 75-78) This invention relates to the refining of lead and lead alloys and has for its object to provide a new and improved process of removing partly or completely from impure lead or lead alloys some or all of any of the following impurities or constituents, viz. arsenic, tin, zinc, selenium, tellurium, manganese, copper, iron, cobalt, cadmium, nickel and antimony.

According to the present invention the improved process consists in removing in a single operation and in the following order from impure lead or lead alloys while in a molten condition and in the presence of molten caustic alltali any desired plurality of the following impurities or foreign metal constituents when present, namely: arsenic, tin, zinc, selenium, tellurium, manganese, copper, iron, cobalt, cadium, nickel and antimony, by using, as reagent with the molten caustic alkali, lead sulphide in an amount at least requisite for effecting removal to the desired stage. The amount of lead sulphide used may be limited to substantially that stoichiornetrically requisite, or it may be in excess but in the latter case the operation must be stopped when the desired stage of removal is reached.

The impurities or foreign constituents in the lead become progressively removed therefrom and appear as sulphur compounds in the caustic soda whilst the lead component of the lead sulphide reagent passes into and becomes part of the lead bath.

The lead sulphide reagent may conveniently be the readily available mineral galena and can be used in its natural state in granulated or powered condition as de rived from a dressing or mechanical separation of the lead sulphide from the crude ore. The molten caustic alkali may be caustic soda.

it will be appreciated that the reagent in the form of galena is much cheaper than chemically fabricated lead sulphide, and in fact the additional metallic lead which the galena adds to the lead bath is more valuable that the galena itself. The lead content in galena is commonly recovered in a crude form by subjecting the dressed ore to a smelting process, the crude lead thus obtained being afterwards remelted and refined by one of the known processes. It will be apparent that, by using the dressed ore as the reagent in the present invention the smelting operation, with its attendant disadvantages of slag and fume formation, is avoided and the invention therefore provides an improved method of reducing lead sulphide, particularly galena, to metallic lead.

A great advantage of the process of the present invention is that it is preferably carried out at a temperature of only 300-350" C. in contrast to all other thermornetallurgical lead refining processes. This temperature is suficient to maintain both the impure lead and the caustic soda in a molten condition and to promote the reaction between the galena, the caustic soda, and the impurities or foreign constituents in the lead or lead alloy. However, the aforesaid temperature range is not to be regarded as limitative, as a somewhat higher tem- 2,843,476 Patented July 15, 1958 perature may be adopted in the interest, for example, of greater fluidity and/or time occupied.

The molten caustic soda will naturally tend to float on the surface of the molten lead and means are therefore provided to ensure that the lead sulphide and caustic soda are brought into intimate contact with the whole of the molten lead. For this purpose the lead sulphide may be placed upon the surface of the molten caustic soda and the requisite contact between the lead sulphide, the caustic soda, and the lead bath, may be effected by means of a stirring or agitating device within the lead bath or by circulating the molten lead through the molten caustic soda and galena by withdrawing the lead continuously or at intervals and re-introducing it to the reaction vessel so that it returns to the bath.

As already mentioned, the removal of the impurities or foreign constituents takes place in the particular order stated. For example, if the impure lead is one containing, say, arsenic, tin, zinc and copper, the first three can be removed, leaving the copper in the lead, by using only sufficient lead sulphide (galena) to remove them, or by using an excess but stopping the process at the end of the zinc removal stage.

it is to be noted that antimony is the last metal in the list and it is well known that substantially pure antimonial lead, i. e. lead-antimony alloy, is in great demand cornmercially. it will therefore be appreciated that the process is particularly valuable-in producing antimonial lead from impure lead containing not only antimony but some or all of the other metals enumerated. Either an excess of lead sulphide (galena) is used and the process is stopped a just before the antimony removal stage is reached, or

just sufiicient galena is used to remove all of the impurities except the antimony.

The following examples indicate some results obtained by the process:

Examples 1 and 2 indicate the removal of the commoner impurities, arsenic, tin, copper and antimony. EX- amples 3 to 7 indicate the removal of the less common impurities which in some instances, and for the purpose of demonstration only, were actually introduced into the lead before starting the removal treatment, and in these examples it is to be understood that the effect of the treatments on the commoner impurities if present would be substantially on the lines indicated by Examples 1 and 2.

Example 1 9,106 grammes of lead alloy containing 0.02% Sn, 0.104% Cu, 0.135% As, 7.92% Sb, balance Pb, were treated in 5 stages with altogether 4,000 grammes of NaOI-I and 2,925 grammes of galena containing 74% Pb, 11% S. The resulting metal assayed at the various stages as follows:

Sn Cu As Sb Pb 0. 02 0. 0001 5. 73 Balance 0.0007 0. 0001 r 1. 27 Do.

The recovered lead weighed 10,453 grammesand the spent salt weighed 5,330 grammes. Of the lead inputas alloy-kgalena--99.l7% was recovered as refined lead and 0.65% was in the spent salt.

Example 2 9,000 grammes of lead alloy containing 2.30% Sn, 0.28% Cu, 0.32% As, 7.22% Sb, balance Pb, were treated in 5 stages with 4,820 grammes of 'NaOH and 3,120 grammes of galena. The resulting metal assayed at the various stages as follows:

Sn Cu 1 As I Sb I Pb stage 1 0.03 0. 0.03 7. 02 lzalaute stage 2 0. 005 0. 007 0. 001 4. 60 D0. stage 3. 0. 005 0.0015 0. 001 2. D0. stage 4t 0. 005 0.0006 0. 001 0.33 D0. stage 5 0. 0002 0.0005 0. 00002 0. 0005 D0.

The recovered lead weighed 10,430 grammes and the spent salt weighed 6,350 grammes. Of the total lead input-as alloy+galena-98.9% was recovered as refined lead and 0.80% was in the spent salt.

Example 3 This demonstrates the removal of cadmium and zinc. 9,010 grammes of lead alloy containing 2.00% Sn, 0.35% Cu, 0.142% As, 7.35% Sb, 0.51% Cd, 0.51% Zn, balance Pb, were treated in 2 stages with 2,400 grammes of NaOH and 1,600 grammes of galena. The resulting alloy assayed as follows as regards to cadmium and zinc contents:

Cd Zn stage 1 .Q stage 2 0.002. not detectable.

Example 4 This demonstrates the removal of selenium and tellurium. 4,600 grammes of lead alloy containing 0.116% Se, 0.10% Te, 7.0% Sb, 0.08% Cu, balance Pb, were treated in one stage with 625 grammes of NaOH and 300 grammes of galena. The resulting alloy assayed as follows as regards the selenium and tellurium contents: Se not detectable, Te not detectable.

Example 5 This demonstrates the removal of nickel. 5,00 grammes of alloy containing 2.92% Sn, 1.18% Cu, 0.157% Ni, 0.121% As, 9.65% Sb, balance Pb, were treated in 5 stages With 3,000 grammes of NaOH and 2,120 grammes of galena. The resulting metals assayed as follows as regards nickel content:

This demonstrates the removal of manganese and cobalt. 5,000 grammes alloy containing 2.9% Sn, 5.74% Sb, 0.0146% Mn, 0.013% Co, 0.085% Cu, 0.3% As, balance Pb, were treated in 4 stages with 2,100 grammes of NaOH and 1,600 grammes of galena. The resulting metals assayed as follows as regards the manganese and cobalt contents:

stage 1 0. 0005 0.0016 stage 2 0. 0005 0. 0012 stage 3 0. 0001 0.0009 stage 4 0. 00004 0. 0006 Example 7 This demonstrates the removal of iron. 5,000 grammes of lead alloy containing 1.0% Sn, 5.70% Sb, 0.066% Fe, balance Pb, were treated in 4 stages with 1,900 grammes of NaOH and 1,300 grammes of galena. When assayed, the resulting alloys gave the following iron contents:

In all cases, the temperature at which the treatments took place was 300-350 C. The time occupied for each stage varies from 30 to 60 minutes.

The procedure for removing the impurities or foreign constituents may be to treat the impure lead or the lead alloy with successive separate quantities of molten caustic soda and galena as indicated by the above examples and to recover the metals respectively from the several quantities of spent reagent, or alternatively to treat the impure lead or the lead alloy with a single bulk of caustic soda and galena and then treat the spent bulk of reagent for separation of the different metals which are present within it either as insoluble suspensions (sulphides) or as dissolved thio-salts as the case may be. For example, arsenic, tin, antimony and selenium will be present in the caustic soda as water-soluble thio-salts, whereas zinc, copper, nickel, cobalt, cadmium, manganese, iron and tellurium will be present as sulphides insoluble in water. Whichever method of recovery of the metals is adopted, the spent molten caustic soda may be granulated in the usual way and filtered to separate liquor from insoluble residue.

The accompanying drawings illustrate in diagrammatic form two embodiments of apparatus suitable for carrying out the process. In these drawings Figure 1 is a sectional elevation of one embodiment and Figure 2 is a sectional elevation of the second embodiment.

In Figure 1 the reference numeral 1 indicates a heated pot containing molten lead 2. 3 is a rotary stirrer for agitating the lead and causing a vertical motion as indicated by the arrows. 4 is a chute for the delivery of canstic alkali reagent onto the molten lead in the vicinity of its vortex so that it becomes well mingled with the lead, and 5 is a chute for the delivery of granulated galena. 6 is the layer of molten caustic alkali and galena riding on the molten lead. 7 is an outlet and valve for the final removal of the lead, and 8 is an overflow outlet and valve for the reagent.

In Figure 2 the same reference numerals are used for the same parts as in the apparatus of Figure l, and it will be observed that instead of the rotary stirrer of Figure 1, the apparatus of Figure 2 includes a circulating pump 9 connected to the pot at its lower end for driving the molten lead up a delivery pipe 10 to a distributing rose 11 which continuously spreads a part of the molten lead into the molten reagent riding on the bulk of the molten lead in the pot, it being understood that in this construction as the distributed lead gravitates through the molten reagent it becomes intimately exposed to reaction therewith.

I claim:

1. The process of treating impure lead and lead alloys containing a plurality of metal impurities which consists in substantially removing from the impure lead or lead alloy, while in a molten condition and in the presence of molten caustic alkali, a selected metal impurity present by pursuing the treatment through the substantial removal of metal impurities, as far as they are present, in the following ordcr until the said selected metal impurity is reached and substantially removed, namely, arsenic, tin, zinc, selenium, tellurium, manganese, copper, iron, cobalt, cadmium, nickel and antimony, by subjecting the impure lead or lead alloy at a temperature of from 300 to 350 degrees Centigrade, to vigorous mixing action with dressed and granulated mineral galena as reagent with the molten caustic alkali, in an amount, as predetermined stoichiometrically, to substantially remove the said selected metal impurity together with such of the anteriorly enumerated metal impurities as are present.

2. The process of treating impure lead and lead alloys containing a plurality of metal impurities which consists in substantially removing from the impure lead or lead alloy, while in a molten condition and in the presence of molten caustic alkali, a selected metal impurity present by pursuing the treatment through the substantial removal of metal impurities, as far as they are present, in the following order until the said selected metal impurity is reached and substantially removed, namely, arsenic, tin, zinc, selenium, tellurium, manganese, copper, iron, cobalt, cadmium, nickel and antimony, by subjecting the impure lead or lead alloy to vigorous mixing action with lead sulphide as reagent with the molten caustic alkali in an amount as pre-determined stoichiometrically that is at least just requisite to substantially remove the said selected metal impurity, together with such of the anteriorly enumerated metal impurities as are present.

3. The process according to claim 1, applied to impure antimonial lead, which consists in carrying out the said treatment with an amount of the said galena that is just requisite, as pre-determined stoichiometrically, to substantially remove all of the metal impurities enumerated as may be anterior to antimony, whereby the resulting antimonial lead will be free of the said impurities.

4. The process according to claim 2, applied to impure antimonial lead, which consists in carrying out the said treatment with an amount of the said sulphide that is just requisite, as pre-determined stoichiometrically, to substantially remove all of the metal impurities enumerated as may be present anterior to antimony, whereby the resulting animonial lead will be free of the said impurities.

References Cited in the file of this patent UNITED STATES PATENTS 1,025,956 Asbeck May 14, 1912 2,217,981 Hallows Oct. 15, 1940 2,543,041 Meyer Feb. 27, 1951 OTHER REFERENCES Handbook of Nonferrous Metallurgy, Liddell, Graw-Hill Book Co., 1110., 1945, pages 174-175. 

1. THE PROCESS OF TREATING IMPURE LEAD AND LEAD ALLOYS CONTAINING A PLURALITY OF METAL IMPURITIES WHICH CONSISTS IN SUBSTANTIALLY REMOVING FROM THE IMPURE LEAD OR LEAD ALLOY, WHILE IN A MOLTEN CONDITION AND IN THE PRESENCE OF MOLTEN CAUSTIC ALKALI, A SELECTED METAL IMPURITY PRESENT BY PURSUING THE TREATMENT THROUGH THE SUBSTANTIAL REMOVAL OF METAL IMPURITIES, AS FAR AS THEY ARE PRESENT, IN THE FOLLOWING ORDER UNTIL THE SAID SELECTED METAL IMPURITY IS REACHED AND SUBSTANTIALLY REMOVED, NAMELY, ARSENIC, TIN, ZINC, SELENIUM, TELLURIUM, MANGANESE, COPPER, IRON, COBALT, CADMIUM, NICKEL AND ANTIMONY, BY SUBJECTING THE IMPURE LEAD OR LEAD ALLOY AT A TEMPERATURE OF FROM 300 TO 350 DEGREES CENTIGRADE, TO VIGOROUS MIXING ACTION WITH DRESSED AND GRANULATED MINERAL GALENA AS REAGENT WITH THE MOLTEN CAUSTIC ALKALI, IN AN AMOUNT, AS PREDETERMINED STOICHIOMETRICALLY, TO SUBSTANTIALLY REMOVE THE SAID SELECTED METAL IMPURITY TOGETHER WITH SUCH OF THE ANTERIORLY ENUMERATED METAL IMPURITIES AS ARE PRESENT. 